1. Field of Invention
This invention relates to pressure gauges using a cylindrical vibrator wherein fluid pressure or differential pressure applied to the vibrator affects the resonance frequency of the vibrator. More particularly, this invention relates to such a pressure gauge which is resistant to external pressures and vibrations and which is highly accurate and reliable, and which may be used extensively, for example, and especially effectively, in aircraft applications.
2. Description of the Prior Art
FIG. 1 is a partially broken perspective view of a conventional, cylindrical vibrator type pressure gauge of the type to which this invention is applicable. This pressure gauge comprises a cylindrical vibrator 10, a cylindrical body 11 disposed within vibrator 10 and a driving coil 21 for driving vibrator 10 and a detector coil 31 for detecting vibrations of the vibrator 10. The coils 21 and 31 are installed on the body 11 as depicted. Vibrator 10 is housed in a cylindrical protective cover 4. Pressure P.sub.i (e.g. pressure of a fluid or gas), undergoing measuremment is admitted into the inside of vibrator 10 through an inlet hole 51. Vibrator 10 is so constructed that its resonance frequency varies in accordance with the difference between pressure P.sub.i and the pressure within the chamber between vibrator 10 and cover 4, that is the pressure outside of vibrator 10, which may be the reference pressure.
The conventional device of FIG. 1 has cylindrical body 11 holding coil 21, which acts to vibrate vibrator 10 and holding coil 31 for detecting the resonance frequency. One end of body 11 is a free end. Consequently, body 11 can have natural frequencies in a direction perpendicular to the axial direction. Thus, the resonance frequency of vibrator 11 is undesirably affected thereby. Furthermore, in order to increase resistance to pressure, the side wall and the end portion of vibrator 10 are required to be thick, which lowers the natural frequencies of the vibrator in a direction perpendicular to the axial direction of the vibrator. The result is that the conventional device is more susceptible to external vibrational noise.